1. Field of the Invention
The present invention relates to the generation of three-dimensional CG (computer graphics) moving images, and more particularly to a stereoscopic CG moving image generating apparatus capable of presenting the viewer with proper motion and depth perception according to the camera and subject motions, magnitude of motion parallax, and display viewing conditions.
2. Description of the Prior Art
An example of a prior art stereoscopic CG image generating apparatus is shown in FIG. 9. According to this apparatus, three-dimensional structural information, describing a three-dimensional shape of a subject by a surface model, is input (the subject is approximated by a plurality of small surfaces called polygons, the structural information defining the three-dimensional positions of the vertices of each polygon and the faces and edges formed by the polygons), and the subject defined by this information is arranged in a world coordinate system. Then, projection transformation sections 1 and 2 calculate the two-dimensional positions of the subject that would be projected on a film when photographed by an imaginary camera, and rendering sections 3 and 4 determine the brightness and color (e.g., R, G, B values) of an image within each polygon on the basis of the material of the subject, the type of the light source used, and the three-dimensional positions.
For example, a geometric model of a polyhedron, such as shown in FIG. 10(a), is described by the three-dimensional coordinates of vertices V1 to V8 and the data structure (forming faces and edges) of the geometric model, as shown in FIG. 10(b), and the subject described by this information is arranged in the world coordinate system such as shown in FIG. 11(a).
That is, an image (more specifically, vertices) of the subject projected on a screen 50, as viewed from viewpoint E of the camera, is calculated. Then, the positions on the screen of the faces and edges formed by the vertices and their brightness and color are calculated to produce an image for output.
At this time, in order to produce a stereoscopic image, images as viewed from at least two viewpoints must be calculated; as shown in FIG. 11(b), camera parameters are described by the viewpoint positions of cameras CL and CR, the spacing Wc between the plurality of cameras, the three-dimensional coordinates of the converging point P of the cameras in the case of converging shooting, and the focal length f of the cameras (or the field of view .theta.).
The above description essentially concerns the generation of a still CG image. When generating moving CG images with the cameras and subject moving, the images are generated one by one by sequentially changing the motion parameters of the cameras and subject. A camera sequence generating section 5 and an object sequence generating section 6 are provided to store and supply this sequence data.
However, with the above prior art stereoscopic CG image generating apparatus, the motion parameters of the plurality of cameras and the motion parameters of the subject, if not properly adjusted, may often not match the visual functions of the viewer, straining the visual system of the viewer.
For example, for a human to be able to perceive motion on the screen without unnaturalness, it is desirable that the moving velocity of target objects be held within a certain value. Furthermore, to provide proper depth perception by motion parallax (relating to the relative velocity between a plurality of target objects), the relative velocity also must be limited. This requirement is also related to the size of a displayed image and the viewing distance. Accordingly, the prior art has had the problem that unless these parameters are always set correctly, improper images are generated that can cause unnaturalness and can lead to fatigue and eyestrain.
In view of the above problem of the prior art stereoscopic CG image generating apparatus, it is an object of the present invention to provide a stereoscopic CG moving image generating apparatus that can automatically generate natural-looking and easy-to-view stereoscopic images for a viewer regardless of the viewing distance and screen size.